Hydraulic fluid



Patented July 22, 1941 UNITED STATES PATENT OFFICE HYDRAULIC FLUIDArthur G. Weber, Wilmington, Del., assignor to E. I. du Pont de Nemours& Company, Wilmington, Del., a corporation of Delaware No Drawing.Application April 24, 1936, Serial No. 76,205

8 Claims.

' absorbers, brake mechanisms, artillery recoil mechanisms, liftingjacks, door checks, etc.

While mechanisms of this class differ in details of construction, theiroperation involves similar principles and they also present commonpractice problems by reason of similarity of operating parts andconditions of use. Metal cylinders and rubber cups or washers are commonto most commercial devices of the class and one of the importantpractical problems is that of providing a fluid, for use therein, whichwill not produce corrosion of metal and deterioration of rubber.

Various compositions including one or more of vegetable, animal, andmineral oils, alcohols, ethers, etc. have been prepared and used withvarying degrees of success but, so far as I am aware, no presentcommercial fluid satisfactor ily meets the aforementioned requirements.

I have found that the desired freedom from metal corroding and rubberdeteriorating properties is possessed to a surprising degree by a classof substances not heretofore employed in hydraulic fluids, viz. aspecific class of esters of acids, derivable from vegetable and animaloils preferably containing oleflnic linkages and/or hydroxyl groups,such as the acids present, in free state or as esters, in such oils as:almond, blackfish, candle-nut, castor, China-wood, cocoanut, cod, corn,cottonseed, croton, eucalyptus, geranium, grape seed, hemp, juniper,lard, lemon, linseed, maize, menhaden, neats foot, olive, orange, palm,peanut, pine, porpoise, rape seed, seal, sesame, shark, sperm, tallow,train, .sunflower, tung, turpentine, walnut, whale, wool, and the like.The foregoing class of substances has also the important property ofleaving upon metal surfaces of operating parts a thin protective film,which reduces metal corrosion to a substantial degree. I

. The esters of the foregoing derivation which are comprised in myinvention are the mono-esters of monoand dior triatomic alcohols and themonoor diesters of dior triatomic alcohols such as the monoand diglycoland glyceryl esters, the alcohol having, preferably, not more than fivecarbon atoms per molecule.

More specifically and preferably however, I utilize the monoanddiglycerides and glycolides of vegetable oils such as the monoordiglycerides or glycolides of soya bean oil acids or the monoanddiglycerides or glycolides of castor oil acids, 1. e., glycol orglyceryl monoand diricinoleates.

To provide properties of fluidity desirable where extremes oftemperature are encountered, the esters referred to such as the glyceryland glycol monoand diesters, may advantageously be admixed with one ormore solvents or diluents, preferably organic, of low freezing point.For

' this purpose I may use: alcohols, such as the Ill monoand polyhydric,aliphatic, alicyclic, aromatic and amino alcohols, such as methanol,propanol, isobutanol, octanol, diacetone alcohol, ethylene and propyleneglycol, glycerol, sorbitol, cyclohexanol, phenol, benzyl alcohol,triethanolamine and ethoxyaminobutanol; organic esters such as ethyl andbutyl acetate; ethers such as diisobutyl, ethyl tertiary butyl andmethyl ricinoleyl ethers; alcohol ethers, such as ethyleneglycolmonoethyl ether and diethyleneglycolmonoethyl ether; aldehydessuch as heptaldehyde and benzaldehyde; ketones, such as diisopropylketone and cyclohexanone; nitrogen-containing compounds such astriethanolamine, octyl amine, tetrahydrofurfuryl alcohol and furanecompounds; hydrocarbons, such as isooctane, benzene, and cyclohexane.

Solvents or diluents as above illustrated may be used in ratios to theester which vary over a wide range, although, generally speaking, Iprefer to have at least about 10% of the ester present in the finalcomposition.

As examples of representative hydraulic fluids of this invention. I havefound that the following compositions have highly desirablecharacteristics:

Example 1 Percent by volume Isobutanol '75 Glyceryl monoricinoleate 25Example 2 Percent by volume Isobutanol a- 56.25 Glycerine 13.5 Propyleneglycol 20.5 Glyceryl monoricinoleate 10.00

Example 3 Percent by volume Isobutanol 62.5 Diethylene glycol 22.5 Water15.0

To parts of the above mixture was added 20 parts glycerylmonoricinoleate.

Percent by volume mixture is heated for a length oftime suflicient forall the castor oil to react completely. Complete reaction takes placeafter heating from 1-2 hours and may be determined, if desired, in amanner such as set forth in Example 11. The final product, whichcomprises substantially ethylene glycol monoricinoleate, is admirablysuited Ethyl alcohol 50 Glyceryl monoricinoleate 50 Example 7 Percent byvolume Ethyleneglycolmonoethyl ether 65 Glyceryl monoricinoleate 35Example 8 The glyceryl monoricinoleate of Examples 1--'! inclusive, maybe replaced by a like amount of glyceryl diester of ricinoleic acid, orof the mix ture of oleic, linoleic and palmitic acids obtainable fromsoya bean oil.

Example 9 Percent by volume Branched chain aliphatic alcohols (obtainedby pressure catalytic hydrogenation of carbon oxide) boiling 147-157" C50 Soya bean oil monoglyceride 50 Example 10 Per cent by volume Branchedchain aliphatic alcohols (obtained by pressure catalytic hydrogenationof carbon oxide) boiling 147-157 C 50 Soya bean oil diglyceride 50Example 11 As an example only, typical of the procedure, which maybefollowed in the case of any alcoholic body-oil mixture according tothis invention, 15 parts by volume of castor oil and 32 parts propyleneglycol are heated, using a concentration of approximately 4% potassiumoleate as a catalyst, at 180-200 C., for a time sumcient for all theoriginal oil to react completely. Whether or not all the oil has reactedmay be readily determined, for example, by utilizing the fluid as anelectrical resistance and noting when no further change in saidresistance takes place. At that point it will be found that all the oilhas reacted with the alcohol or alcoholic body. I have found that fromto 2 hours heating is sufiicient and that from 1-2 hours is preferable.

I may use this product as such but prefer to mix it with an equal volumeof butyl alcohol (normal or iso) The product resulting from the heattreatment comprising substantially propylene glycol monoricinoleate ismixed to the extent of 47 parts by volume with 53 parts isobutanol ornormal butanol to give a complete hydraulic fluid of highly desirablecharacteristics. 4

Example 12 24.3 parts by volume of castor oil and 32 parts by volume ofethylene glycol are heated at 170- 190 C., while using as a catalyst aconcentration of approximately 2% lead oxide by weight. The

for use in hydraulic apparatus, but preferably I mix it in the ratio of47 parts by volume with 53 parts by volume of isobutanol.

Example 13 14.5 parts by volume of castor oil and 32 parts by volume ofpropylene glycol are heated at 150-175" C., 4% by weight of potassiumoleate being used as a catalyst,-for 1-2 hours. At the expiration of theheating all the castor oil has completely reacted with the glycol (whichmay be determined as set forth in Example 11) to give a fluid comprisinga greater part propylene glycol monoricinoleate which is, by itself,well adapted for use with hydraulically operated apparatus. I prefer,however, to mix equal volumes of normal butanol with the final product.

Example 14 24.3 parts by volume of grape seed oil and 32 parts by volumeof ethylene glycol are heated at ITO-190 0., while using as a catalyst aconcentration of approximately 2 lead oxide by weight. The mixture isheated for a length of time sufllcient for all the grape seed oil toreact completely. Complete reaction takes place after heating from 1-2hours and may be determined, if desired, in a manner such as set forthin Example 11. The final product, which comprises the greater partethylene glycol monooleate and linoleate, is admirably suited forhydraulic apparatus but, preferably, I mix it in the ratio-of 47 partsby volume with 53 parts by volume of isobutanol.

Hydraulic fluids are used under a wide range of climatic and artificialconditions involving a considerable range of temperature, pressure, andthe like. For example, such fluids when used in automotive mechanismsoperate at temperatures that may vary from -50 F. to above F. This, inturn, requiresfluidity at low temperatures and at the same timesuflicient viscosity to permit operation at high temperatures.

In order to comply with all these requirements I have found that in thecase of certain individualdiluents it'may be desirable to add asolubilizing agent to the ester-diluent mixture, and in such cases Ihave found that various materials or combinations of materials aresuitable. Thus, for example, such compounds as alkyl ricinoleates, e. g.ricinoleyl hydroxy stearate, glycol stearate and octyl-2 methyl pentylricinoleate, or the higher, branched chain alcohols obtainable by thecatalytic hydrogenation of oxide of carbon, such as 2-5 dimethyloctanol-l, 4-7 dimethyl pentanol-2, andthe like, are effective assolubilizers.

Another method of solubilization according to this invention isaccomplished by the use of emulsifying agents which produce permanentminutely divided two phase systems, e. g. by the use of celluloseethers, methyl or ethyl cellulose, glycol cellulose, polyalcoholderivatives, such as glycol stearate, alcoholic amines such as ethanolamines, and the like.

The lubricating qualities of the hydraulic fluids of this invention maybe even further improved by the addition of assisting lubricants, suchas defiocculated graphite, or extreme pressure luthe like; metal soapssuch as potassium oleate,

and the like.

These assisting lubricants have a particularly Q advantageous value inlowering the pour point at temperatures slightly above that at which thelubricant solidifies.

In like manner as the lubricating qualities of the fluids of thisinvention may be improved, corrosion of the operating parts with whichthe fluids come in contact, if ordinarily occurring, may be overcome byuse of corrosion'inhlbitors, without adversely afiecting theadvantageous characteristics of my fluid. Various materials may beutilized for inhibition of corrosion which, in some instances, also fillthe role of assisting lubricants, such as above described, and/or otheradditional functions. Thus, for example, I may utilize alkali metaloleates, ricinoleates, abietates, arsenites, benzoates, phosphates,chromates, isopropyl sulfonates, dichromates, nitrites, dior triethanolamines, glucamines, sulfurated castor oil, sulfonic acid salts of oleicacid, Gardinols. and the like as corrosion inhibitors.

The proportion of corrosion inhibitor to the' hydraulic fluid proper maybe widely varied, particularly if it is also acting to fulfill otherfunctions, such, for example, as those of anassisting lubricant. Iprefer, however, to utilize the corrosion inhibitor in relatively smallquantities such as not greatly exceeding, say, 0.2-5% of the totalcomposition.

' In order to obtain a fluid, such as previously described, whichpossesses suflicient body at the extremes of temperature that may beencountered in automotive operation, it is sometimes desirable, inpreparing the fluid, to add materials as bodying agents, such as metalstearates, particularly aluminum, calcium and magnesium stearates,cellulose compounds, such as masticated cellulose, glycol cellulose, andmethyl cellulose, gum tragacanth, cyclohexanolamine stearates, alginicacid salts, and the like.

Similarly materials may be added, which depress the pour point of thefluid, such as octadecsuspensions of graphite in castor oil, known-underthe trade-marked name Castordag," suspensions of graphite in water knownunder the trade-marked name of Aquadag, suspensions of graphite inglycerine known under-the tradeanediol ether, molasses, glucose,sorbital, the

aminophenol, pyrogallol and amines such as 2, 4-

diamino-i-hydroxy diphenyl amine, paraaminodiphenyl amine, phenylalphanaphthylamine, diphenylamine, and the like. I

Various changes may be made in the present invention without departingtherefrom or sacrificing any of the advantages thereof.

I claim:

1. A fluid for use in fluid pressure apparatus, including at least 10%of a substance from the group consisting of glyceryl monoand diesters ofvegetable and animal oil acids and glycol esters of said acids, togetherwith a liquid aliphatic monohydric' alcohol and a liquid aliphaticpolyhydric alcohol. 1

r 2. A fluid for use in fluid pressure apparatus, including at least 10%of a substance from the group consisting of: glyceryl monoand diestersof vegetable and animal oil acids and glycol esters of said acids,together with isobutanol and a glycol.

3. A fluid for use in fluid pressure apparatus, including at least 10%of a substance from the group consisting of: glyceryl monoand diestersof vegetable and animal oil acids and glycol esters of said acids,together with isobutanol and propylene glycol.

4. A fluid for usein fluid pressure, apparatus, including at least 10%of glyceryl monoricinoleate, together with appreciable amounts ofglycerine, propylene glycol and isobutanol.

5. A fluid for use in fluid pressure apparatus including at least 50% byvolume 01' a liquid monohydric alcohol, atleast 20.25% of a liquidaliphatic polyhydric alcohol and at least 10% of a substance selectedfrom the group consisting of glyceryl monoand di-esters of vegetable andanimal oil acids. v

6. A fluid for use in fluid-pressure apparatus including at least 50% byvolume 01' a liquid aliphatic monohydric alcohol, at least 20.25% of aliquid glycol, and at least 10% of glyceryl monoricinoleate.

7. A fluid for use in fluid pressure apparatus including at least 50% byvolume oi a liquid aliphatic monohydric alcohol, at least 20.25% of

